1. Field of the Invention
The present application relates in general to the field of core-stiffened structures.
2. Description of Related Art
Composite structures often comprise honeycomb core disposed between and adhesively bonded to an inner skin and an outer skin. One example of such honeycomb core is a honeycomb core 101, shown in FIG. 1. Generally, honeycomb core 101 includes a plurality of cells 103 (only one labeled for clarity) defined by cell walls 105 (only one labeled for clarity). Each of the plurality of cells 103 exhibits a width W. Typically, the plurality of cells 103 have substantially the same width W but, in some implementations, some cells 103 of the plurality of cells 103 may have different widths W than other cells 103 of the plurality of cells 103.
Traditionally, core-stiffened structures have been limited to the use of honeycomb core 101 having cell widths W of less than about 6 mm. At larger widths W, as shown in FIG. 2, cell walls 105 fail to provide sufficient support for inner skin 201 and outer skin 203 during “curing” of the core-stiffened part, which entails heating the assembled core-stiffened part under pressure. As a result, portions of inner skin 201 and portions of outer skin 203 undesirably extend into cells 103 of honeycomb core 101. Thus, while core-stiffened structures made from larger-celled honeycomb core 101 weigh less than similar structures made from small-celled honeycomb core 101, the manufacture of large-celled composite structures has been limited.
Traditionally, core-stiffened composite structure has been sealed from intrusion of moisture. Some typical core materials are subject to moisture absorption or corrosion resulting from trapped moisture within the core. The sealing, of the core edges is done by ramping one skin along a bevel in the core until both skins contact each other and complete a seal around the periphery of the core. During the cure cycle, the pressure on the ramp surface of the core may push the core in a direction lateral to the tool. In order to prevent such a distortion of the core, typically material is added to the skin in the proximity of the ramp in order to stabilize the skins from lateral distortion of the core during the cure cycle. As such, the skin is thicker than the structural application requires so as to prevent lateral distortion of the core during the cure cycle.
A similar situation exists for core stiffened composite structure where one skin is not parallel to the other skin. Such a scenario includes the risk of the core material being pushed laterally along the tool surface. In order to prevent such a distortion of the core material, additional material is added to the core material and/or to the skins in order to resist the lateral force, and therefore resist core distortion.
There are many methods for processing honeycomb core composite structures well known in the art; however, considerable room for improvement remains.
While the application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the application to the particular forms disclosed, but on the contrary, the application is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the application as defined by the appended claims.